In hair treatments such as hair rinses and hair conditioners, it is practiced to lower the pH of their systems to impart luster and softness to hair. No attempt has, however, been made to lower the pH of hair cleansing compositions, because the hair cleansing compositions are intended to impart neither luster nor softness in general.
With a view to providing hair cleansing compositions with functions to give such luster, softness and manageability as described above, the present inventors conducted research on low-pH hair cleansing compositions which made use of organic acids. A problem, however, arose in that in a low pH range, anionic surfactants as cleansing ingredients underwent decomposition, resulting in stability deterioration such as gelling of systems and reduction in foamability. On the other hand, hair itself has a buffer capacity. A simple application of a treatment to hair, therefore, leads to a change in the pH of the treatment solution, raising a problem that its intended effects cannot be fully brought about.